Open Source Headless CMS
A headless CMS draws a clean line - content in a database with an API, presentation left to whatever front end you want - which is freeing until you realize that decoupling also makes your content model a long-term commitment, painful to move once a thousand entries depend on it. The open source options here keep the content store, the schema, and the API on infrastructure you run, so the editorial data your whole front end consumes stays in a database you own and query directly rather than fetch by subscription.
Strapi
Model content visually and Strapi generates REST and GraphQL APIs with a self-hosted admin
Payload
A Next.js native headless CMS that installs in your app folder with a TypeScript backend
Directus
Wraps any SQL database in instant REST and GraphQL APIs, a no-code admin app, and auth
TinaCMS
Git-based headless CMS that edits Markdown, MDX, JSON, and YAML with a GraphQL API
KeystoneJS
Define a content schema in code and get a GraphQL API plus an admin UI for Node.js
Webiny
Self-hosted headless CMS that runs on AWS serverless and is extended with TypeScript
Gentics Mesh
Headless CMS built around content trees, with REST and GraphQL APIs and Elasticsearch search